The invention relates generally to drug infusion systems and, more particularly, to a syringe driver for expelling fluid from a syringe and a syringe for use in the syringe driver.
Syringe drivers are used in the medical environment to infuse a given dose of a medicament into a patient from a syringe engaged with the driver. The medicament is generally infused at a regular rate over a period of time which may vary from, for example, an hour to a number of days. Referring to FIG. 1, a conventional ambulatory syringe driver 10 comprises a housing 12 which includes a rotatable threaded shaft or lead screw 14 driven by a motor located within the housing. The motor is powered by batteries also located in the housing. The threaded shaft 14 is exposed and a driver block 16 with a threaded bore is mounted on the threaded shaft such that rotation of the shaft drives the driver block along the shaft. The driver block is provided with a de-clutch button 18 which, when depressed, de-clutches the driver block from the threaded shaft to allow free movement of the driver block along the shaft. The driver block has a clip or slot 20 by which a plunger 22 of a syringe 24 can be secured to the driver block for controlled movement of the plunger 22.
While FIG. 1 represents a typical current ambulatory syringe driver system, some non-ambulatory systems have differences. In such non-ambulatory syringe driver systems, the lead screw and driver block are enclosed within the casework of the device, usually running parallel to, but spaced apart from the syringe barrel. An arm or slide extends sideways from the driver block out through the casework, to engage the syringe plunger. The arm terminates with a plunger holder, which usually incorporates a mechanism for remotely de-clutching the half nut within the driver block. Thus, a driving force can be applied to the syringe without exposing the lead screw. Additionally, many such non-ambulatory systems are powered by both main power (wall power) and battery power.
In the operation of the syringe driver shown in FIG. 1, a syringe having a cylindrical syringe body and a plunger slidably mounted in the body is clamped 26 to the housing by its body. The free end of the plunger extends from the syringe body and lies parallel with, but spaced apart from, the threaded shaft. The de-clutch button 18 is depressed to allow free movement of the driver block along the threaded shaft such that the slot in the driver block is aligned with and receives the free end of the plunger. Once the free end of the plunger has been secured to the driver block, the de-clutch button is released and the driver block once again engages the threaded shaft. When the motor of the driver is actuated, the driver block is driven towards the syringe body thereby driving the plunger into the syringe body causing fluid in the syringe body to be expelled and infused into the patient.
A disadvantage of such a syringe driver, as described above and shown in FIG. 1, is that the overall size of the syringe driver with respect to the syringe is large. This is due at least in part to the driver block that is mounted on the threaded shaft. In particular, the driver block 16 accounts for a significant portion of the overall size of the syringe driver 10 in that it spaces the syringe plunger 22 away from the threaded shaft 14 and requires an additional length to the threaded shaft to accommodate the driver block when the largest syringe specified for the driver 10 is used and the driver block must be moved to the far end of its travel to receive the plunger of that syringe. This is necessary because of the internal components of the driver block, such as the de-clutch button 18, the internal threaded portion, and the slot 20 of the driver block. The threaded portion must be long enough to firmly engage the threaded shaft and must have means to hold the threads in contact with the threaded shaft even under heavy loads provided by the syringe or downstream infusion system. However, certain applications, such as ambulatory uses, would benefit from a smaller size syringe driver system.
Another disadvantage associated with conventional syringe drivers is that there is a certain amount of play between the driver block 16 and the threaded shaft 14 which gives rise to hysteresis in the movement of the block with respect to the threaded shaft as well as some backlash. It should be noted that the driver block, as well as the housing, motor, threaded shaft, and syringe clamp are all reusable elements. Because the driver block is a reusable element, such hysteresis and backlash tend to worsen over time because of wear on the driver block. It would also be of value to lessen the possibility of wear of the driver block.
Additionally, driver blocks, depending on their complexity, can themselves add a significant expense to the syringe driver system. Further, should replacement due to wear be required, the labor needed to disassemble the syringe driver housing, as well as the “down time” of the syringe driver system to replace the driver block are undesirable costs for a hospital or other health care institution. Thus, an improvement over existing driver block designs would be desirable, as well as making syringe driver systems smaller to make them more useful in an ambulatory application.
Many ambulatory syringe drivers presently available are calibrated in millimeters per hour; i.e., a distance rate, as they lack the complexity to determine the size of syringe fitted. Most medical infusion prescriptions are written in volume to be infused; i.e., milliliters per hour. Having to convert milliliters per hour to millimeters per hour can impose an additional undesired step on medical care providers. However, most non-ambulatory syringe drivers are calibrated in milliliters per hour as they tend to be fitted with systems that can identify the syringe type by its external diameter. It would be of benefit to provide an ambulatory syringe driver system that can automatically recognize the syringe installed and can therefore accept a flow instruction in volume per time format, such as milliliters per hour to make setting the rate of infusion easier.
Additionally, it is also convenient for a pump or driver to present the care provider with a warning that the syringe is nearly exhausted. This has been found to be beneficial when the preparation of a patient's medicants takes some time but cannot be prepared too far ahead of time. With a near-end-of-infusion warning, preparation of those medicants can begin. As mentioned above, ambulatory syringe drivers typically lack complexity and in most cases, do not include a mechanism to determine the near end of infusion point. They usually only provide an alarm at the end of infusion when the syringe is exhausted. Some non-ambulatory devices however have mechanisms to determine not only the existence of linear movement of the syringe plunger but also the near-end-of-infusion point and these features would be desirable in ambulatory designs as well.
Hence, those skilled in the art have recognized a need for a syringe driver system having a reduced size as well as one with fewer moving parts subject to wear and replacement. Additionally, an ambulatory syringe driver system light and small enough to be carried by a person and capable of receiving infusion instructions in volume per unit time as well as one that detects linear movement of the syringe plunger and provides a near end of infusion warning have been recognized as needed. It has also been recognized by those skilled in the art that it would be of value to have a syringe driver system that is lower in cost and easier to manufacture. The present invention satisfies these needs as well as others.